1. Field of the Invention
The present invention is related to a method and apparatus for mounting a plurality of circuit elements such as integrated circuits and memory elements on a printed wiring board. In particular, the present invention is directed to a terminal density conversion board and connection structures for integrated circuits mounted on the printed wiring board.
2. Description of the Related Art
In recent years, high-speed, low-cost multi-chip modules (MCM) having a plurality of integrated circuit parts mounted on high-density printed wiring boards have become the subject of industrial attention. These multi-chip modules are classified roughly into three types: MCM-L, MCM-C, and MCM-D. The MCM-L type mounts circuit elements on a printed wiring board allowing reductions in production costs. The MCM-C type mounts circuit elements on a thick-film multi-layer ceramic board achieving a moderately high speed at a low cost. The MCM-D type module has circuit elements installed on a circuit board having laminated dielectric and conductive wiring layers on a thick-film substrate such as a ceramic board.
These multi-chip modules are mounted on printed wiring boards (also referred to as circuit boards) together with other circuit elements, which may include active elements such as LSI chips, resistors, and capacitors.
Mounted parts, such as the multi-chip modules and the other circuit elements, have many terminals. The pitches or distances between the terminals of these mounted parts are fixed values. The terminals of these mounted parts are connected to the terminals formed on a printed wiring board. The terminals on the printed wiring board are connected with the multi-layer wiring inside the printed wiring board.
The speed and performance of circuit elements, such as multi-chip modules, mounted on printed wiring boards can be rapidly increased, as compared with other mounted parts, resulting in a radical miniaturization and proliferation of terminals. Naturally, reducing the size of the interterminal pitch on such circuit elements has thus become necessary. Correspondingly, for printed wiring boards on which such mounted parts are mounted, the reduction of the interterminal pitch length is deemed to be inevitable. That is, the interlayer connecting vias formed on a baseboard must be very dense (i.e., tightly packed together) to be used for printed wiring boards for such increasingly faster and improved multi-chip modules.
The printed wiring board is generally a large baseboard, because many circuit elements are mounted thereon. It is extremely difficult to install the highly dense vias over the total area of the baseboard uniformly and flawlessly. Therefore, the yield for this kind of printed wiring board is lower than that of boards forming lower density vias, and this increases the production cost of the overall structure including the mounting parts (such as multi-chip modules) and printed wiring boards on which these mounting parts are mounted.